The aim of this paper is to study the corrosion inhibition of magnesium in hydrochloric acid by using tween 80 surfactant. The inhibition action of tween 80 was studied using hydrogen evolution and weight loss methods. It was found that the addition of tween 80 surfactant inhibits the corrosion rate. The inhibition action was expounded on the basis of adsorption of tween 80 on the magnesium surface forming a hindrance of mass and charge transfer leading to protect the magnesium surface from the aggressive ions. The values of adsorption thermodynamic parameters were calculated and explained. Moreover, theoretical calculation for the energetic parameters and natural bond orbital charges for the tween 80 have been done using hybrid density functional theory B3LYP. The calculations show that non-homogenous branching in tween 80 is more stable compared to homogenous one by about 0.36 eV which can be related to steric hindrances. The theoretical calculations showed that during the physical adsorption, partial electronic charge are transferred from magnesium surface to LUMO orbital which is localized on the ester group.